Field of the Invention
The present invention relates to a flash band determination device, a method of controlling the same, a storage medium, and an image pickup apparatus, and more particularly to a flash band determination device that determines whether or not there is a flash band caused by an external flash of light in an image obtained through image pickup.
Description of the Related Art
In recent years, as an image pickup device used in an image pickup apparatus, such as a video camera, a CMOS image sensor (hereinafter referred to as the CMOS sensor) is used. In general, compared with a CCD image sensor (hereinafter referred to as the CCD sensor), the CMOS sensor is advantageous not only in that it is easy to manufacture, but also in that it consumes less power, and so forth. Further, there is also proposed a CMOS sensor increased in frame reading speed by increasing the number of read-out channels.
The CMOS sensor uses a so-called rolling shutter method in which horizontal lines are sequentially exposed, and video signals (image signals) are sequentially read out on a line-by-line basis to thereby generate one frame. In the CMOS sensor using the rolling shutter method, the exposure timing for each line and the read-out time for each line are out of synchronization. For this reason, if there is an external flash of light emitted in a very short emission time period, such as a so-called flash or a strobe light, there is generated, depending on a location on the screen, an image in which one frame is divided into an upper belt-like area and a lower belt-like area different in brightness, over two frames, in other words, there is generated an image in which a bright area caused by the external flash of light is split between two frames. Such a step of brightness between the belt-like areas caused by the external flash of light is referred to as the flash band.
On the other hand, in a case where the CCD sensor is used, the above-mentioned flash band is not generated, so that even when an external flash of light is used, it is possible to obtain an image which is uniformly bright throughout one frame and is free from a sense of strangeness. For such a reason as described above, an image pickup apparatus using the CMOS sensor is equipped with a correction function for correcting a flash band.
For example, there has been proposed an image pickup apparatus configured to detect a flash band so as to correct the same (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2009-253367). In this image pickup apparatus, a change in luminance is calculated, and if the change in luminance corresponds to substantially one frame, it is determined that a flash band has occurred.
However, when performing determination of a flash band using the method described in Japanese Laid-Open Patent Publication (Kokai) No. 2009-253367, if there is an object which is constantly bright and extends horizontally, it is difficult to perform determination of a flash band.